FIGS. 1–6 illustrate the prior art crossover tool in a typical gravel packing operation. The wellbore 10 receives a running string and setting tool shown schematically as 12. A packer 14 sealingly accepts the string and setting tool 12. A ball seat 16 is located in the crossover tool 18 just above gravel pack port 20. Screen extension 22 is attached to packer 14 and has ports 24 to permit gravel access to annulus 26. Screen extension 22 has a seal bore 28 through which a wash pipe 30 extends in sealing contact for run in, shown in FIG. 1, due to contact of seals 32. A flapper 34 allows uphole flow in wash pipe 30 and prevents downhole flow. Return ports 36 are in the seal bore 38 of the packer 14 and are closed due to the position of seals 40 that straddle return ports 36 in seal bore 38. Screen extension 22 has a support surface 42 that can engage tabs 44 to pinpoint the circulation position of FIG. 4.
To set the packer 14, the assembly is run into position, as shown in FIG. 1 and a ball 46 is dropped onto ball seat 16. Ultimately, after the packer is set, the ball 46 is blown through ball seat 16 or the ball and the seat move together after a shear pin (not shown) is broken and the assembly lands in recess 48 (see FIG. 3). One of the problems with this layout is that if the formation is under sub-hydrostatic pressure, such sub-hydrostatic pressure communicates with the underside of ball 46 on seat 16 and limits the amount of pressure that can be applied from above, shown schematically as arrows 50, before breaking a shear pin on the ball seat 16. This can reduce the available pressure to set the packer 14 because the sub-hydrostatic pressure on the underside of ball 46 acts equivalently to applied pressure from above, represented by arrows 50. Yet another drawback of this arrangement is that when the packer 14 makes contact with the wellbore 10 and the passage through its seal bore 38 is obstructed, the liquid column above the packer 14 can no longer exert pressure on the formation. This can result in portions of the formation breaking off into the wellbore and potentially obstructing it. The present invention addresses these problems by repositioning the ball seat 16′ and insuring that the seal bore 38′ is not closed by the crossover tool 18′ during setting of the packer.
Continuing now with the prior technique, after the packer 14 is set, the ball 46 and the seat 16 are blown into recess 48. The set of the packer can be tested by applying pressure to annulus 54. Furthermore, gravel slurry or fluid represented by arrows 52 can be squeezed into the formation adjacent to the screens (not shown) as illustrated in FIG. 3. The fluid represented by arrow 52 flows through the crossover tool 18 to exit the gravel pack port 20 and then flows through ports 24 in screen extension 22 into the annulus 26 around the outside of the screens (not shown). Returns are blocked off because the return ports 36 are sealingly positioned in seal bore 38 of the packer 14 by virtue of straddle seals 40. Any leakage past packer 14 will be seen as a pressure rise in annulus 54.
The next step is circulation, shown in FIG. 4. Here the gravel slurry represented by arrows 56 passes through the crossover 18 through gravel pack ports 20. It then passes through ports 24 in screen extension 22 and into the annulus 26. The gravel remains behind in annulus 26 around the screens (not shown) and the carrier fluid, represented by arrows 58, passes through the screens and opens flapper 34. It should be noted that the crossover 18 has been raised slightly for this operation to expose return ports 36 into annulus 54 above packer 14. The carrier fluid 58 passes the flapper 34 and exits the return ports 36 and goes to the surface through annulus 54. Lug 44 rests on support surface 42 to allow the crew at the surface to know that the proper position for circulation has been reached.
In the next step, called evacuation, the excess gravel that is in the annulus 70 between the screen extension 22 and the crossover tool 18 needs to be reversed out so that the crossover tool 18 will not stick in the packer seal bore 38 when the crossover tool 18 is lifted out. To do this, the crossover tool 18 has to be lifted just enough to get the evacuation ports 60 out of seal bore 28. Evacuation flow, represented by arrows 62 enters return ports 36 and is stopped by closed flapper 34. The only exit is evacuation ports 60 and back into gravel pack port 20 and back to the surface through the sting and setting tool 12. The problem here is that the intermediate position for reversing gravel out from below the packer 14 is difficult to find from the surface. Due to the string 12 being long and loaded with gravel at this point, the string is subject to stretch. The surface personnel for that reason are prone to wittingly or unwittingly skip this step and pull the crossover tool 18 up too high into the alternate reverse position shown in FIG. 6. In the FIG. 6 position, the evacuation ports 60 are closed in seal bore 38 of packer 14 and gravel pack port 20 is now above packer 14 in annulus 54. Arrows 64 show how the reversing flow clears out the string 12 above packer 14.
The problem with skipping the evacuation step is that the excess gravel in the annulus 70 below packer 14 may cause the crossover tool 18 to stick in seal bore 38 as the crossover tool 18 is raised to accomplish the reverse step shown in FIG. 6 or later when crossover tool 18 removal is attempted. The present invention allows the evacuation step to occur without having to reposition the crossover tool 18 with respect to the packer 14. This is accomplished by the addition of check valves 66 in relocated evacuation ports 60′. The present invention will be more readily appreciated by those skilled in the art from a review of the description of the preferred embodiment and the claims that appear below.